The present invention relates to redundant arrays of independent disks (RAID), and in particular to mechanisms for cabling two controllers to the same disk drives.
In RAID systems, often two different controllers are each connected to the same group of disk drives for redundancy. In a typical configuration, each controller is coupled to a number of hubs. Each of the hubs may be connected to up to four disk drive enclosures. Each enclosure can include as many as twelve disk drives. Since both controllers need to connect to the same disk drives, the hubs must connect to the same enclosures, thus multiple connections are required. Because the significant amount of cabling involved, there is the possibility for cabling errors in connecting the disk drives.
In a typical configuration, each enclosure of twelve disk drives will have one or two disk drives that include SCSI enclosure services (SES). This capability essentially allows the SES device to poll the other devices in the enclosure to determine their identities and slot assignments, as well as other configuration data.
It would be desirable to be able to automatically determine that the cabling is correct such that each of two redundant controllers identifies the same disk drives in the same locations to facilitate a smooth transition of control from one controller to the other.
The present invention provides a method and apparatus for determining proper cabling and identical device locations between two controllers in a RAID system. Each controller first obtains the port names of the devices to which it is attached. The list is then reviewed to determine that there are no duplicate entries. Once this step is completed, the controllers exchange their port name lists. The lists are compared to make sure they exactly match. Finally, the controllers exchange a map of the devices themselves present on two channels connected to the ports. The exchange device maps are compared and must be equal. The two device maps being equal indicate that each storage device is logged on to the network through both I/O ports and is available to each controller.
In a preferred embodiment, the port names in the first steps are the ports of at least one, and preferably two, SES polling devices in each disk drive enclosure. The SES polling devices themselves determine the identity of the devices in their enclosures, and pass this along to the controllers.
For a further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings.